The present invention relates to drying compressed air and more particularly, to a double directional check valve and flow restrictor combination which is capable of drying compressed air, nitrogen or other process gas for use in the production of semiconductors.
In the semiconductor production industry, clean dry air, nitrogen and other gases are frequently used in the processing of semiconductor wafers. These processing gases typically must contain a very low moisture content in order to prevent manufacturing defects in the integrated circuits on the wafers. For example, during the semiconductor fabrication process, a semiconductor die is attached to a leadframe and encapsulated in plastic. Any moisture remaining on the semiconductor wafer from the semiconductor processing steps can be absorbed from the semiconductor wafer into the package interior and lead to one of several failure mechanisms.
A minimum package moisture content accepted in the semiconductor industry is 0.04 percent, or {fraction (1/2500)} of the total weight of the package. Any moisture content which exceeds this level may cause a xe2x80x9cpopcornxe2x80x9d failure, in which the moisture is vaporized and increases the internal pressure of the package. Consequently, the package may pop or fracture along the seams. Replacing the semiconductor device is expensive and time-consuming, and may result in damage to the printed circuit board.
A moisture absorbing-type drying system is commonly used in the semiconductor industry for drying compressed air, nitrogen or other process gas. This type of drying system uses dessicant to produce dry air from air having a relatively dry moisture content. The system uses two check valves and a flow restrictor which are installed as separate units. The valve housings, flow restrictor housing and connecting piping for the system occupy a relatively large volume of valuable space. Furthermore, poor purge efficiency in such systems increases operating costs due to waste of purge air.
It is therefore an object of the present invention to consolidate usage of space in the production of clean, dry air, nitrogen or other process gas.
Another object of the present invention is to provide a flow restrictor and check valve combination in a single housing.
Still another object of the present invention is to provide a double directional check valve and flow restrictor combination which is capable of drying compressed air, nitrogen or other process gas for use in the production of semiconductors.
Yet another object of the present invention is to provide a double directional check valve and flow restrictor combination which can be easily and conveniently installed.
A still further object of the present invention is to provide a double directional check valve and flow restrictor combination which is simple in construction.
Yet another object of the present invention is to provide a double directional check valve and flow restrictor combination which enhances purge efficiency to save purge air volume and cost in a compressed air drying system.
Another object of the present invention is to provide for constant flow of air for the drying of desiccant in an air drying system.
In accordance with these and other objects and advantages, the present invention comprises a T-shaped housing which contains a pair of axially-aligned check valves and a flow restrictor disposed between the check valves. Dry purge air flows into the housing through the flow restrictor, which facilitates smooth and uniform flow of the air, and out of one of the check valves to a dessicant chamber to dry or regenerate dessicant in the chamber. The housing is fitted with flanges or other connection structures for quick, easy and convenient attachment of the housing to a piping network in an air, nitrogen or other process drying system.